Working up of sulfide iron ores



Oct. 27, 1959 E. Kuss ETAL 2,910,343

WORKING up OF SULFIDE mow ORES Filed Aug. 11. 1953 GRANULA TED ORE STEAM STEAM GENERATOR S- REC UPERA TOR 2 gzlrma GAS 3 w DRIER A $02-6AS 3 DOUBLE GATE 7 7 A w n L uoum SULFUR 4 900 REACT/ON FURNACE 7000 F BLOWER P EHEA ER DOUBLE GATE 5 R T 6 REG LAT/N6 VALVE INVENTORS: ERNST KUSS, OSKAR EMERT, ALFRED DIE TR/CH. ARNOLD RBELHANS ZIRNG/BL United States Patent WORKING UP 0F SULFIDE IRON ORES Ernst Kuss, Oskar Emert, Alfred Dietrich, and Arnold Elbe], Duisburg, and Hans Zirngibl, Leverkusen, Germany, assignors to Duisburger Kupferhuette, Duisburg, Germany Application August 11, 1953, Serial No. 373,546

' Claims priority, application Germany August 18, 1952 9 Claims. (Cl. 23-224) This invention relates to improvements in the working up of sulfide iron ores.

The conversion of metal sulfides into sulfur and metallic oxides with sulfur dioxide at a temperature in excess of 600 C. is known. It is further known that by using relativelylarge quantities of additional agents, as, for example, 25-50% of magnesium oxide, iron oxide, and aluminium oxide, or sulfates of such metals, the conversion may be accelerated. It is also known that the conversion may be improved by increasing the concentration of sulfur dioxide used. It has been set forth that a particularly economical point is reached with an amount of sulfur dioxide equal to 50%. It is further stated that an addition of steam brings about a substantial improvement in the reaction velocity.

The process in which sulfur dioxide is produced by air at the base of a shaft furnace charged with coke and pyrites, and this sulfur dioxide is reduced at the head of the furnace with iron sulfide or coke into sulfur, has been described. The heat content of the hot gases at the head of the furnace, which consist predominantly of nitrogen, is utilized to effect the thermal dissociation of the pyrites into iron sulfide and sulfur. The product recovered by this process is converted into copper matte.

In the literature of the art there is also described the sulfatizing of non-ferrous metals in sulfide ores, in which the ores are thoroughly roasted in a first stage with air and sulfur dioxide concentrated up to 10% in the presence of coal. This drives the sulfur content off as elemental sulfur. In a second stage, the sulfatizing of the ore is effected with a mixture of air with a least 10% sulfur dioxide in co-current at a temperature about 700 After the sulfur has been removed, the quantities of sulfur dioxide necessary for the enrichment are removed from the waste gases of the combined furnace, are concentrated, and conducted back into the furnace. In one process it is stated that the reaction is effected without external heating. 1

In accordance with another-description in the literature, practically pure oxygen is used to liberate elemental sulfur from sulfide ores. In accordance with this method, sulfur dioxide which is formed in addition to the metallic oxide, is recycled by a gas circuit into the process. The addition of oxygen is adjusted automatically by the decrease of pressure caused by the condensing of sulfui' vapor in the circuit. It is stated that it is unnecessary to measure or control the addition of oxygen by valves or similar means to keep it in suitable proportion to the metal content to be oxidized. Furthermore, in accordance to this process, only the oxygen is heated before entering into the reaction furnace. Almost the entire heat requirement for the reaction must be obtained by the exothermic reaction of the ore with oxygen. This cannot be realized on a technical scale'if this oxidation is limited to the formation of iron oxide and does not comprise simultaneously sulfur.

One object. of this invention is a new method for the 2,910,348 c6 Patented Oct. 21, 1959 recovery of sulfur, metallic oxides and metallic sulfates from sulfide ores. This, and still further objects will become apparent from the following description, read in conjunction with the drawing which diagrammatically shows an embodiment of a plant set-up for effecting the process in accordance with the invention.

In accordance with the invention, elemental sulfur is successfully recovered from sulfide iron ores and preferably pyrites, while at the same time metal oxides and metallic sulfates are recovered.

In accordance with the new process, a circuit gas which contains more than sulfur dioxide to be reacted with the ore is preheated to a temperature in excess of 500 C. before being passed into the reaction furnace. 1 The oxygen content of this circuit gas is maintained between 2% and 8% at the entry into the reaction furnace. This will result in a temperature betwen 800 C. and 1000 C. in the lower region of the furnace.

The circulating sulfur dioxide may suitably be heated in a heat-exchanger or cowper stove by external means.

Sulfide iron ore, predominantly in the form of granules or pellets of 220 mm. diameter, is worked up in a reaction furnace as is shown in the accompanying drawing. The ore, whether in the form of natural run of mine lb or in the form of granules 1a, the way of manufacturing which is set forth further down, is heated in the presence of non-oxidizing gas in a drier 2 from 20 to 500 C. and charged via double gate 3, where it has a temperature of still about 400 C., into the reaction furnace.

The preheating of the ore is carried out, in the first place, for drying, in the second place, for driving off and, icircumstances permitting, collecting the volatile coustituents of the ore such as arsenic, selenium and antimony, the sulfides or halides of which; in the third place, for improving the heat balance of the subsequent reactions in the furnace of the ore with the reaction gas by the heat content of the heated ore.

The reactions having been finished, that is to say, when the sulfide sulfur content of the ore has been converted into sulfur vapor as completely as possible, when the iron content has been converted into iron oxide as completely as possible and the non-ferrous metal content into leachable compounds, above all into sulfates, the ore charge leaves the furnace through the power double gate 5, and in so doing, it cools from about 700 to 400C.

The reaction gas consists of over 90% sulfur dioxide. It is led and circulated by a blower C, heated from about C. to a predetermined temperature between 500 and 800 in a heat exchanger D with external heating, and admixed with 28% by volume of oxygen with the aid of a regulating valve 6 at the points E or E" before or after heating. The fed oxygen is partly converted into the corresponding equivalent of sulfur trioxide.

Between the ore and the reaction gas, predominantly the following reactions take place in the furnace from top to bottom:

S endothermic reaction S endothermic reaction SFeS-l- 2O Fe O +3/2 S exothermic reaction 2CuFeS +5O 2 CuSO +Fe Q CuO+SO +S2 exothermic reaction Me S+2O MeSO exothermic reaction with Me standing for any divalent metals such as zinc,

cobalt, cadmium etc.

The addition of oxygen to the reaction gas will convert the iron component of the ores into iron oxides, preferably into ferric-ferrous oxide (Fe O and the non-ferrous metal components into the corresponding sulfates. Thus the quantity of it in proportion to the quantity of the ore is determined. The concentration of the oxygen in the reaction gas is accurately regulated by a regulating means such as a valve. The concentration of the oxygen in the reaction gas varies within the limits stated from 28% by volume according to the composition of the ore, to the adjustment of the maximum temperature of the charge from 800 to 1000", to the quantity of the reaction gas and to the physical properties of the ore. For the same ore, at a fixed optimum temperature, the oxygen concentration is adjusted and maintained constant at i 0.5% deviation. The combination of the preheating of the reaction gases and their reaction with the mono-sulfides of the material permits the control and adjustment of the exothermic and endothermic reactions in the furnace in-a highly desirable manner, so that the sulfur content of the ores may be recovered without losses caused by undesirable and uncontrollable oxidations. At the same time a roasted ore cinder is produced which contains less than 5% sulfide sulfur.

The new process allows the keeping of the reaction temperature at the lower part of the furnace well over 800 C. without adding detrimental additives such as coke to the ore and without loss of sulfur oocuring by oxidation and without sintering or smelting the charge. The temperature in the furnace may be regulated and is maintained below the sintering temperature of the material by regulation of the temperature and composition of the gases introduced. The process is particularly advantageous for obtaining a complete continuous treatment of lumpy ores.

The heat content of the gases streaming upward from the lower to the upper portion of the furnace is utilized to remove the disulfide sulfur from the pyrites, which, in turn, causes the temperature of the reaction gases to fall below 650 C. Thus the exothermic oxidation of the monosulfides is coupled with the endothermic heat decomposition of the disulfide sulfur, as, for example, from the pyrites in an economically advantageous manner. The oxygen-free reaction gas charged with sulfur vapor leaves the reaction furnace at A and is passed to a recuperator or steam generator B, where the heat content of the gas is utilized for the generation of steam by cooling to 150. During the cooling liquid sulfur is separated off and withdrawn in the liquid form in a bottom trough H. The gas freed from sulfur is then heated up to 500 C. and led back into the reaction furnace by an adjustable blower after the addition of the predetermined amount of oxygen.

To effect a complete sulfatization of the non-ferrous metal content, the ores should preferably be finally ground before they are passed into the reaction. The granulation or pelletising is so effected in the known manner that the finely ground ore is fed into a rotating drum, where it is sprayed with a liquid. Thereafter the ore, while on its way through the drum, is formed into 220 mm.-diameter pellets or spheroids.

In accordance with the invention, highly concentrated, i.e. half-concentrated to 9/ 10-concentrated aqueous solutions of salts such as magnesium chloride, magnesium sulfate, aluminium sulfate, sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, or double salts thereof, are used as such a liquid in the granulation process in amounts of 5-15% by weight of the ore charge. Thus, these salts are most finely divided in the dried granules in amounts of 15% by weight of the ore. They catalytically favor the development of sulfur and the sulfatization of the non-ferrous metals. Moreover, such solutions of salts in the dry granules serve as mechanical hardening agents. Furthermore, the said salts promote the driving oil? of arsenic from the ore in a nonoxidizing atmosphere between 400 and 500".

4 The following examples are given by way of illustration and not limitation:

Example I Pyrites grains of 615 mm. diameter and containing 46.9% S, 41.1% Fe, 1.0% Cu, 0.9% Zn and 0.57% As were heated in an externally heated furnace up to 600 C. with circuit sulfur dioxide. 30 liters S0 were used to 1 kilogram of pyrites. At 600 C. 2.5% oxygen was added to the circuit gas and the gas circuit so regulated that the gas passed through the charge 34 times per hour. In this way the oxygen was completely absorbed by the metal components of the ore without the sulfur being oxidized into sulfur dioxide. During the reaction, the temperature in the ore charge increased to 800 C. and was maintained constant by regulating the supply of oxygen within the limits of 2.4 and 2.6% by volume of the entering gas. of the charged sulfur was recovered as elemental sulfur.

Example 2 kilograms of broken pyrites of 5-15 mm. sized grains and containing 48.1% sulfide sulfur were treated hourly in a reaction furnace. During a reaction time of 10 hours 900 C. was attained and maintained with a total charge of 4500 m circuit gas, which, on entering the reaction furnace, had a temperature of 650 C. and was mixed with 4.85.3% by volume of oxygen. 42 kilograms=87.5% of elemental sulfur was obtained per hour, While 2.3 kilograms:4.8% of sulfur in the form of sulfates were present in the discharged roasted material.

Example 3 Granules of between 6 and 10 mm. diameter were produced from a finely-ground ore of the following composition: Fe 40.9%, S 47.0%, Cu 3.4%, Zn 2.4%, Pb 0.2%, Co 0.1%, and As 0.1%. The granules were heated for 30 minutes in the presence of inert gas: up to 450 C. and fed into a reaction furnace in hourly charges of 80 kilograms. There they were further heated with the reaction gas which was preheated up to 600 C., whereby a reaction temperature of 840 C. was reached and maintained by the regulated addition of oxygen in a ratio between 6.0 and 6.4% by volume. In the course of a reaction time of 24 hours, 38.6 kilograms of sulfur were obtained per hour=82% yield.

The thoroughly roasted ore contained non-ferrous metals in an easily leachable form, while the iron content of the ore up to 0.2% of the charge was present as insoluble iron oxide.

Example 4 100 kilograms of pyrrhotite of the following chemical composition were hourly fed into a reaction furnace in continuous operation: S 34.2%, Fe 50.5%, Zn 4.2%, Cu 2.1%, remainder gangue. One half of the charge consisted of broken ore of 3-12 mm. sized grains, the other of granules of 69 mm. diameter. On entering the furnace, the reaction gas had a temperature of 530 and consisted of S0 91%, 2.22.3% by volume of free oxygen, 1.5% by volume of S0 remainder nitrogen and carbon monoxide. In continuous operation, 27 kilograms of elemental sulfur=79% of the sulfur content in the ore was obtained per hour.

After leaching the soluble non-ferrous metal compounds, 0.09% Cu and 0.18% Zn, remainer iron oxides and gangue, were still present in the roasted ore.

Example 5 Flotation pyrites of under 0.25 mm. sized grains and of the composition as in Example 1, was wetted in a rotatrng granulating drum by a sprayer with 4 different hquids, formed into pellets of 610 mm. diameter by rolling, and further treated as in Example 3.

For the granulation were used on to 1 kilogram of ore:

In case (a) 60 com. Mgcl -solution (with 270 grams of MgCl on to 1 liter of solution, half-concentrated) In case (b) 90 ccm. MgSO -solution (with 300 grams of MgSO on to 1 liter of solution, 9/ 10 concentrated) In case 50 com. carnallite-solution (with 200 grams of MgC1 KCl on to 1 liter of solution, 7/70 concentrated) In case (d) 80 ccm'. water.

The granules of cases (a), (b), (0) showed a -10-fold higher resistance to compression and abrasion compared to those which were produced from ore and water. On heating for 40 minutes at 480 in a non-oxidizing atmosphere, 65% of the arsenic content of the granules became volatile in case (a), 38% in case (b), 70% in case (0), and 7% in case (d). When these granules were subjected to roasting under the same conditions as in Example 3, the recovery of sulfur achieved was:

In case (a)=96% of the theoretical yield, In case (b)=92% In case (c)=93% In case (d)=84% The conversion of the non-ferrous metal components into soluble salts ran parallel to the recovery of sulfur.

We claim:

1. Process for the recovery of sulfur, metallic oxides, and metallic sulfates from iron sulfide ores which comprises contacting such an ore in a reaction zone with a reaction gas, preheated to a temperature in excess of 500 C. and containing at least 90% sulfur dioxide and an oxygen content of 2-8% by volume, and thereafter recovering sulfur, metallic oxides and metallic sulfates.

2. Process according to claim 1, in which the oxygen is partly replaced by an equivalent of sulfur trioxide.

3. Process according to claim 1, in which said reaction gas is preheated by indirect heat-exchange.

4. Process according to claim 1, which includes granulating said ore prior to said contacting in the presence of 1-5% by weight of a member selected from the group consisting of magnesium chloride, magnesium sulfate, aluminium sulfate, potassium chloride, sodium sulfate, potassium sulfate and double salts thereof.

5. Process according to claim 4, in which said group member is added during said granulation in the form of a highly concentrated solution.

6. Process according to claim 4, in which said granulation is efiected to a grain size of 2-20 mm.

7. Process according to claim 1, which includes utilizing the heat of the reaction gases in said reaction zone to decompose said ores and cool said gases to about 650 C., and which includes cooling the gases: thereafter outside of said reaction zone for the recovery of sulfur.

8. Process according to claim 7, in which the heat removed in said cooling outside of said reaction zone is utilized for the generation of steam.

9. Process according to claim 1, in which said ore is preheated to a temperature between 400 and 550 C. prior to said contacting.

References Cited in the file of this patent UNITED STATES PATENTS 1,567,378 Millar Dec. 29, 1925 1,939,033 Bacon et al Dec. 12, 1933 1,941,592 Bacon et al Jan. 2, 1934 1,974,886 Young Sept. 25, 1934 2,044,960 Tyrer June 23, 1936 2,530,630 Renken Nov. 21, 1950 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,910,348 October 27, 1959 Ernst Kuss et a1.

It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below. I

Column 2, line 44, for "power" read lower column 4, line 67, for ;remainer" read remainder column 5, line 8, .for "7/70" read 7' l0 Signed and sealed this 26th day of April 1960.

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Ofiicer Commissioner of Patents 

1. PROCESS FOR THE RECOVERY OF SULFUR, METALLIC OXIDES, AND METALLIC SULFATES FROM IRON SULFIDE ORES WHICH COMPRISES CONTACTING SUCH AN ORE IN A REACTION ZONE WITH A REACTION GAS, PREHEATED TO A TEMPERATURE IN EXCESS OF 500 C. AND CONTAINING AT LEAST 90* SULFUR DIOXIDE AND AN 